A soft-start circuit is occasionally included in this type of switching power device. The soft-start circuit is arranged for preventing a large rush current from flowing into a switching element (for example, see Patent Document 1). According to the technology described in the Patent Document 1, a soft-start is carried out in response to an input terminal voltage. Thus, it is possible to prevent a rush current from damaging a switching element.
Since the technology disclosed in the Patent Document 1 reads only an input terminal voltage, the technology effectively operates at the time of activating the input terminal voltage. However, the technology disclosed in the Patent Document 1 cannot be applied to the situation where the output terminal voltage suddenly drops in response to some events after the activation of the input terminal voltage and to the situation where the output terminal voltage drops as the input terminal voltage is not affected by the events.
Additionally, the technology disclosed in Patent Document 2 activates a soft-start circuit with reference to an output voltage, and inhibits an overshoot at the time of activating a power source. In other words, the technology in the Patent Document 2 discloses an invention for inhibiting an overshoot at the time of activating a power source. Even when this type of soft-start circuit is applied to the situation when the output terminal voltage suddenly drops from a reference voltage and returns to a restoration voltage, it may not be applicable in view of the properties of discharging voltage from a capacitor in, for example, a soft-start circuit.
[Patent Document 1] JP 2006-325339 A
[Patent Document 2] JP H06-225523 A